1. Technical Field of the Invention
This invention relates to electrical safety devices and, in particular, to an electrical protector module for protecting telephone circuits against excessive voltages and excessive currents.
2. Description of the Prior Art
Telephone circuit protector modules, as exemplified by J. B. Geyer et al U.S. Pat. No. 3,573,695 issued Apr. 6, 1971, are comprised of a pair of assemblies each of which has a spark gap protector for excessive voltages and a heat coil protector for excessive currents. A spring, held in abutment with the heat coil assembly, propels a pin into engagement with a grounding circuit during the passage of excessive currents through the heat coil.
While modules such as this have proved very useful in protecting various telehone circuits from excessive voltages and currents, these protectors exhibit a number of shortcomings. For example, to complete the path to ground the pin in the heat coil assembly must be brought into contact with a carbon block in the spark gap protector assembly. If the current level is sufficiently high, heat is developed in the carbon block assembly. This heat may be sufficient to melt certain plastic elements in the module. In addition, the heat coil assembly is so configured that an insulative member, which electrically isolates a line plate from the grounding circuit during normal operation, can become distorted. This distortion results in intermittent contact with the grounding circuit during the passage of excessive currents through the heat coil pin. A further disadvantage is that the physical arrangement of the heat coil assembly utilizes excessive space within the protector module.
More recent advances in the design of protector modules are illustrated in W. V. Carney U.S. Pat. No. 4,004,192 issued Jan. 18, 1977, and W. V. Carney U.S. Pat. No. 4,004,263 issued Jan. 18, 1977. In the Carney '192 patent the module includes a shaftlike plunger and a coil spring for urging the plunger in a direction toward a carbon block having a recess therein. During normal operation, current is conducted through the spring and plunger to an external contact. Upon actuation of the heat coil, the plunger is moved toward the carbon block and is brought into contact with a laterally extending conductive member, thereby causing conduction from the plunger to ground.
In Carney '263 the module includes a relatively fixed retaining member slidably fitted relative to a plunger similar to that disclosed in Carney '192. In addition, there is an annular compressible electrically conductive member positioned between the retaining member and a portion of the plunger to provide electrical communication between the two irrespective of the relative position between the plunger and the fixed retaining member.
The designs exhibited by the two aforementioned patents are such that internal space must be available to permit the plunger to move into contact with the recess in the carbon block. By virtue of this arrangement, the use of gas tube protectors in place of carbon blocks is precluded. The need for recesses in the carbon blocks further precludes heat shielding of these elements. Since the carbon blocks are provided with recesses, oftentimes tiny particles are produced which drop into the spark gap shorting it out. As a result, normal spark gap type operation is oftentimes precluded.
In addition to the foregoing deficiencies, the placement of the heat coil above the spring in Carney '192 results in a relatively long delicate wire being exposed. This exposed wire can be easily damaged or broken during assembly of the protector.
A more recent example of a protector module is disclosed in G. DeBortoli et al U.S. Pat No. 4,057,692 issued Nov. 8, 1977. The DeBortoli et al patent in general relates to a protector apparatus for telecommunication lines. However, FIGS. 4-9 specifically disclose a protector module. This module is very similar to those designs discussed previously.